Low triiodothyronine in metabolic and inflammatory stress: A context-dependent model of thyroid adaptation

Abstract

Low triiodothyronine status has been described in a wide range of physiological and pathological conditions, including energy restriction, critical illness, and systemic inflammation. In the literature, these alterations are commonly referred to as the low T3 state. Traditionally, they have been interpreted within the framework of the Non-Thyroidal Illness Syndrome (NTIS). However, accumulating experimental and clinical evidence suggests that a similar biochemical phenotype may arise in different systemic contexts through distinct regulatory mechanisms. Thus, low triiodothyronine status may be considered a context-dependent phenotype of systemic adaptation that develops under diverse metabolic and immune conditions.